1. Field of the Invention
This invention is directed to the field of acoustic detection, and more particularly, to a novel method of and apparatus for calibrating hydrophones and detecting vessels acoustically.
2. Description of the Prior Art
Vessels are presently detected using active sonar where a sonic pulse of given frequency or frequencies is reflected off the vessel and returns to the sonar system at essentially the same frequency or frequencies. In many instances, the performance of such sonar systems is limited by interfering reflections from the sea surface and bottom or from inhomogeneities in the water by the mechanism known as volume reverberation.
Conventional acoustic or sonar receiver calibration methods typically use an acoustic projector powered by a local source delivering power to the projector at the desired amplitude and frequency. A hydrophone to be calibrated is positioned at a receiving station away from the projector, It is usually desirable for the receiving station to control the amplitude and frequency of the projected sound. This is typically accomplished by either a wire link connecting the receiving station with the projector or by a voice link to an operator at the projector site.